This invention relates to a mechanism for taking up slack in a vehicle brake system and more particularly relates to a brake slack adjuster which embodies an improved strong and lightweight construction.
Slack adjusters are an integral part of the linkage mechanism for the brake systems on heavy duty vehicles, such as trucks and buses. In the usual arrangement, a slack adjuster is provided for most wheels of a heavy duty vehicle on the shaft through which braking force is applied to the wheel. The slack adjuster responds to the movement of the brake linkage, caused by the application of a force to the braking pedal by the operator, to rotate the brake shaft and thereby apply a braking force through the brake shoes and drum for each wheel.
It is apparent that the slack adjuster is an important element in a vehicle braking system. It must be designed to have substantial strength and durability so that it will repeatedly perform its functions without fail, over a prolonged period of time. At the same time, the slack adjuster must be as lightweight as possible, so that the mechanism does not add unnecessary cost and weight to the brake system and vehicle. Most significant, the dual design requirements of sufficient strength and minimum weight must be met to allow slack adjusters to be provided for an economical cost, and with economical manufacturing techniques, on a high volume, mass production basis.
In addition to effectively transmitting a braking force through the braking system, the slack adjusters must also be readily adjustable. This adjustment feature is necessary to provide the braking system with a mechanism for taking up the slack in the linkage which inevitably results from repeated applications of the brakes in a heavy duty vehicle. The slack adjuster design therefore must provide a solid connection in the brake linkage during normal use and, at the same time, be readily adjustable on the vehicle by a mechanic, with the use of simple and readily available tools.
The environment in which the brake slack adjuster is used also creates substantial design and operation problems. Since a slack adjuster is mounted adjacent the axle housing on heavy duty vehicles, the adjuster is exposed to extreme environmental conditions. The adjuster is subjected to substantial temperature variations, and must continue to function properly in adverse environments such as rain, snow and ice. In addition, the slack adjuster is constantly bombarded by foreign matter such as stones, dirt, mud and salt water which is thrown up from the road by the moving vehicle. Thus, the adjuster must be able to perform its functions of transferring braking force from the brake pedal to the brake shoes and drum while being continuously adjustable despite these extreme environmental conditions. The adjuster also should include means for protecting the mechanism from this adverse environment without the adjustment functions.
The slack adjuster of the present invention alleviates many of the foregoing problems. The present slack adjuster can be forged from high strength steel with a minimum amount of material. The adjuster also is forged to have, in one form, an integral cover plate which eliminates the need for an additional cover plate part. An integral cover plate also improves the operation of the mechanism by providing a complete outer seal on one side of the slack adjuster body. In another form, the slack adjuster is constructed to further enhance its manufacturability and repairability. In this second form opposing sides of the slack adjuster are forged with identically-constructed recesses each for receiving a respective identically-constructed cover plate. The cover plates are fastened within respective recess grooves by peening a rim of the groove down over the peripheral edge of each cover plate.
In yet another cover plate form there is provided a pair of cover plates each with a peripheral skirt flared outwardly so that when inserted in its respective annular groove, and axially compressed, the skirt flares out even more and becomes diametrically enlarged and thus mechanically fixed within the groove. An alternate cover plate usable with the annular groove is constructed out of a resilient material which also includes a peripheral skirt that is initially deformed from its relaxed state prior to installation, so that when fitted within its respective groove and allowed to expand radially outwardly to its relaxed state, it becomes seated firmly within the groove.
A removable protective cap covers the adjustment mechanism to guard the mechanism from the corrosive environment. Moreover, each component can be individually treated with a proven corrosion-resistant material, such as zinc, to minimize the effect of the corrosive environment on the operation and life of the slack adjuster.
The design for the slack adjuster body in accordance with this invention also provides maximum support for the worm wheel included within the body. The worm wheel is an integral link in the transmission of braking force through the slack adjuster, and is subjected to substantial force loads. Accordingly, the life of a slack adjuster is improved, and the wear on the adjuster components is minimized, when the force-transmitting worm wheel is provided with such maximum support. In the same regard, the present slack adjuster design substantially increases the support for the worm gear which meshes with the worm wheel. The worm gear is another component which is subjected to substantial force loads during braking. Thus, improved support for the worm gear likewise prolongs the life of the adjuster mechanism by minimizing wear on the component parts.
The slack adjuster in accordance with the present invention also simplifies the sealing of the adjustment mechanism from the environment. Simple, standard sealing materials, such as flat gaskets or O-ring seals, can be used to protect the internal gear components from contamination by mud, rain, ice, or salt water. The resulting slack adjuster is strong and lightweight, and is relatively inexpensive to manufacture. It also has a prolonged life because of its increased load bearing capacity and its improved sealing features.